A port on an ATM switch is a valuable resource. If a device is designed to interface directly with an ATM switch, but its functionality limits it to using only part of the bandwidth available from its access link, then utilization of this valuable resource can be uneconomical. Furthermore, providing multiple switch ports at some locations may not be convenient, even though more than one device needs access to the ATM network. In order to make more economical use of a port on an ATM switch, other devices in the prior art have been developed. For example, an ATM concentrator is available in the prior art which provides a plurality of ports all centrally located for accessing the ATM port. However, it offers a fixed number of additional ports at a single location so that a user who needs ports distributed throughout a building, for example, would not be able to make efficient use of a concentrator. Furthermore, the number of ports provided by a concentrator is fixed and is not readily modifiable. Another device available in the prior art is the proposed distributed queue, dual bus, for interfacing between an ATM port and a number of peripheral devices. However, this scheme requires modifications to the user interface hardware and an adaptation function. Furthermore, an access protocol overhead on the data transfer phase of a connection is required which reduces the data transfer capabilities.
In order to solve these and other problems in the prior art, the inventor herein has succeeded in designing and developing an ATM interface device which maintains the ATM interface standards and permits multiple devices to share a single ATM access port without interjecting an adaptation function or otherwise interfering with the direct transfer of ATM data between the port and the user's ATM device. With the inventor's interface device, port multiplexing is elegantly simple and preserves the essential operational behavior of the ATM network. It extends the ATM port to multiple interface devices efficiently and transparently and also preserves the functional behavior of ATM channel switching.
In essence, the interface device of the present invention may be readily implemented as a three plug card or board, each of the plugs being designated as either a switch side, device side, or extension side. Each of these "sides" designates the direction of connection for the interface device between the ATM network port and a user's device. As such, it is a building block type of device which permits a user to construct various configurations of sub-networks or busways through which the ATM cells are routed directly to and from connected ATM devices. Each ATM interface device includes a multiplexer to merge ATM data cells into a single upstream data stream and a routing and switching element which generally divides ATM data cell streams into different paths depending upon the configuration of the user constructed sub-networks or busways. A control element processes ATM data cells which are traveling upstream towards the network and either sends them on to the multiplexer or, if they are control cells, sends them to the routing and switching element in order that ATM data cells traveling downstream from the network are properly routed. Routing information for data cells which comprise a VPI/VCI table are stored in a VPXT/VCXT in communication with the routing and switching element. The VPXT/VCXT is updated with control cells received by the control element and transmitted through the routing and switching element.
The interface device of the present invention may be configured in several ways in order to provide different functionality. In the simplest configuration, the interface device may simply be cascaded in order to accommodate the connection of a plurality of ATM devices to a single switch port. In this first configuration, the ATM devices are connected with the switch side of the next succeeding interface being plugged into the extension side of the preceding interface such that they align in a single, unbranched, segment. In a variation of this single segment arrangement, branches may be made by plugging a switch side of an interface into a device side and then plugging additional interfaces using the switch side and extension side connectors as before. In this manner, branches may be made from a single "trunk" in various configurations in order to suit particular installations. This functionality of the interface device of the present invention provides tremendous flexibility to a network manager in building a network with multiple and branched segments. In still another variation, the interface device may be used to substitute for the back plane for a computer to provide direct interconnection between real time data intensive services such as video, audio, and image processing with an ATM network to thereby optimize their functionality. At the same time, a common bus may be utilized for interconnecting a CPU and memory as they are generally viewed as "tightly coupled" such that interconnection through an ATM network would be an inefficient substitute. However, such interconnection could be provided if useful. In still another variation, a ring network or work group of ATM devices may be interconnected using the interface device of the present invention in order to form a stand alone configuration. In this usage, one of the computers interconnected in the ring would need to provide the network control processor overhead, something which would be well known to one of ordinary skill in the art. Lastly, an internal host ATM ring could be formed which would provide an echo feature for viewing, for example, images prior to their being transmitted to the network. In this instance, an interface device would be interconnected between a user and the ATM network in reverse, with the device side being looped back to send the same data cells being transmitted back to the user. Such an interconnection would be desirable if, for example, a user wanted to verify an image or other data prior to its being broadcast over the ATM network.
As is apparent by the short description given in this summary, the inventor's device provides great functionality and is conducive to a number of variations which provide flexibility and features not heretofore known. The interface device itself, and its several different described uses, are more fully explained in the following detailed description of the preferred embodiment.